Since the beginning of modern marine science, oceanographers throughout the world have been plagued by the problem of collecting underwater data. The depths of the ocean, and the inhospitality of that environment to mankind, have made it impossible for scientists to collect data in person in the same manner as their land-bound colleagues. Early in the science, oceanographers used non-mobile sensors attached to cables to probe the depths of the sea. However, these efforts were costly and inefficient, requiring an oceanographic expedition using large research vessels to collect data at limited spatial and temporal scales.
Over the last thirty years, the advent of a variety of underwater vehicles has helped to address these problems. These vehicles include: Remotely Operated Vehicles (ROVs), Unmanned Untethered Vehicles (UUVs), Autonomous Profiling Vehicles (APVs) and Autonomous Underwater Vehicles (AUVs).
Remotely Operated Vehicles (ROVs) used a tether to connect the underwater vehicle to a ship on the surface. The tether was the lifeline for the underwater vehicle, providing power and control signals to the vehicle as well as relaying data back to the operator. ROVs were an incremental gain over their non-mobile sensor counterparts. As long as tether integrity was not compromised, scientists could now move the sensor within a limited range of their craft.
The next class of vehicles, Unmanned Untethered Vehicles (UUVs), removed the problems of the tether. These vehicles replaced the tether with an acoustic, optical, or electromagnetic link to the ship-based operator. The major problem associated with the ROV (the limitation of the tether) had been solved; however, the data transmittal speeds available for underwater craft and their short communications range made these first UUVs highly limited in usefulness.
Autonomous vehicles addressed the limitations of the first UUVs by replacing the need for external operator control with vehicle-based controls. Autonomous Profiling Vehicles (APVs) could function without operator interaction; however, their movement capabilities were restricted to simple vertical movements within a water column. Autonomous Underwater Vehicles (AUVs) are self-propelled vehicles that execute underwater maneuvers autonomously through control signals generated by an on-board computer system. The control signals control the operation of thrusters, actuator-driven control surfaces, and optionally a buoyancy engine. AUVs meet the need for movement in all three dimensions within an ocean environment without operator control.
Much of the work in the prior art has focused on the optimization of AUV subsystems. Specifically, the most recent advancements in technology have focused on hull, navigation, control, communications, and sensor subsystem enhancement.
Prior art AUV hull construction has been of two types. The first, a single pressure hull (usually cylindrical in shape) has all electronics and sensors contained within the hull. The second type, a floodable hull has distinct electronics and sensor modules, each contained within water-tight housings within the hull. In the floodable hull, communications between the modules is accomplished through electrically conducting underwater cables. Both prior art systems have problems. The single pressurized hull does not allow for modular design and implementation of components. However, the flooded hull is more complex to fabricate and has more potential points of failure from water ingress, thereby increasing component sealing costs and failures.
AUV control systems have historically exhibited a wide variety of architectures, with serially distributed intelligent control systems widely favored in recent prior art efforts. Generally, the type of system used for control has been very specifically tailored to the particular AUV. Changes in architecture (for example, from a Complex Instruction Set Computer (CISC) to a Reduced Instruction Set Computer (RISC) Central Processing Unit (CPU) have required significant redesign of all hardware and software. The programming for the control function usually occurs in a lower level language like C or C++. Turn-key operator interfaces for programming AUV dive behaviors have not been implemented, with each dive scenario often requiring lengthy software development.
Communications with the AUV have been important, both for reprogramming the AUV and retrieving collected data; however, AUV communications subsystems in the prior art have been limited. Generally, access to the onboard computer has only been possible through direct physical attachment to a serial port. This means that access can only be achieved after the AUV has been recovered. Some recent prior art AUVs have included towed radio floats with radio antennae to establish a wireless (radio packet modem) connection with the operator upon surfacing. However, towed floats have been problematic for two reasons. First, the float and attachment cable limit the maneuverability of the vehicle and increase the likelihood of cable snags when operating in obstructed waters. Second, the float generally does not project high enough out of the water, resulting in lower transmission range and quality. AUVs are generally equipped with sensors of various types, both to ascertain their location and to make measurements in the ocean.
An industry-wide need exists for a low cost, multipurpose, networkable AUV system. The system should use off-the-shelf components programmable by non-experts in robotics. Also the system should provide sufficient depth range, working time, and behavioral capabilities to match mission requirements across the spectrum of tasks performed by scientists and engineers.